Nitrogen 1

Question 1

What do amino acids and nucleotides contain that carbohydrates and fats don’t?

Answer 1

Nitrogen

Question 2

Where does the nitrogen in our bodies come from?

Answer 2

Our diets

Question 3

How do the plants/animals we eat get their nitrogen?

Answer 3

From nitrogen fixing bacteria known as the diazotrophs.

Question 4

What are the 3 stages called in the nitrogen cycle?

Answer 4

• Fixation
• Assimilation
• Degradation

Question 5

What is the structure of nitrogen?

Answer 5

2 nitrogen atoms are held together by triple bond making it very unreactive

Question 6

How can nitrogen be captured?

Answer 6

• Adding oxygen using lightening to form NO or NO2

- Adding hydrogen using the Haber process to form NH4

Question 7

What are 2 examples of nitrogen-fixing bacteria?

Answer 7

• Cyanobacteria found in Lake Atitlan

- Rhizobium bacteria found on root nodules of legumes

Question 8

What do bacteria require for nitrogen fixation?

Answer 8

• Nitrogenase

- Energy

Question 9

What does the fixation of nitrogen produce?

Answer 9

Un-ionised ammonia (NH3) which in water will exist in equilibrium with ionised ammonium (NH4+)

Question 10

What inactivates nitrogenase?

Answer 10

Oxygen

Question 11

How do nitrogen fixing bacteria get around the abundance of oxygen?

Answer 11

• Live anaerobically

- Some uncouple mitochondria which increases electron flow and ‘burns’ off O2 in the cell

Question 12

How do cyanobacteria prevent O2 entry?

Answer 12

Form heterocysts whose cell walls prevents O2 entry

Question 13

How do leguminous plants allow nitrogenase to work?

Answer 13

They produce leghemoglobin which binds to O2 and keeps the concentration low enough

Question 14

What happens after nitrogen is fixed?

Answer 14

• Soil bacteria convert ammonia to nitrite and then to nitrate.
• Nitrate is taken up by plants and micro-organisms
• Once the nitrate has been taken up it is then converted back to ammonia via nitrite

Question 15

What is the only amino acid that can obtain its nitrogen directly from NH4 and the only one which cn give it up directly?

Answer 15

Glutamate

Question 16

What are the 4 amino acids which are found in higher concentration in cells compared to other amino acids

Answer 16

• Alanine
• Glutamine
• Glutamate
• Aspartate

Question 17

What are the roles of glutamate?

Answer 17

• Excitatory neurotransmitters
• Important in taste
• Amino acid breakdown

Question 18

What is transamination?

Answer 18

Conservation of nitrogen by transferring amino groups between different molecules

Question 19

What are the general principles of transamination?

Answer 19

• No loss or gain of nitrogen
• Readily reversible
• One of the 2 substrate pairs is often glutamate
• Amino acid 1+ Keto acid 2= Keto acid 1+ Amino acid 2

Question 20

What is the difference between an amino acid and a a-keto acid?

Answer 20

• Amino acid has an NH3 group attached to a carbon which is attached to a COOH group
• a-Keto acid has a C double bond O attached to the acidic group

Question 21

What does the reversible nature of transamination allow it to do?

Answer 21

Participate in amino acid synthesis and degradation

Question 22

What do all aminotransferases rely on?

Answer 22

Pyridoxal phosphate cofactor

Question 23

What typically accepts amino groups?

Answer 23

a-ketoglutarate

Question 24

What acts as a temporary storage of nitrogen?

Answer 24

L-glutamine

Question 25

What can L-glutamine do?

Answer 25

Donate the amino group when needed for amino acid biosynthesis

Question 26

What is pyridoxal phosphate?

Answer 26

-Cofactor made from vitamin B6

Question 27

What does pyridoxal phosphate do?

Answer 27

Transfers the amino acid group during the reaction

Question 28

What does the presence of aminotransferases in the plasma indicate?

Answer 28

Cell damage as they are intracellular proteins

Question 29

What aminotransferases are particularly good indicators of cell damage

Answer 29

• Aspartate aminotransferases (aspartate to oxaloacetate)

- Alanine aminotransferases (alanine to pyruvate)

Question 30

How is liver disease monitored?

Answer 30

Measuring serum levels of alanine aminotransferase or aspartate aminotransferase

Question 31

What is a significant energy yielding pathway in carnivores?

Answer 31

Oxidation of amino acids

Question 32

Where do micro-organisms get their nitrogen from?

Answer 32

Scavenged from their environment

Question 33

What are the 3 circumstances that amino acids undergo oxidative catabolism?

Answer 33

• Leftover amino acids from normal protein turnover are degraded
• Dietary amino acids that exceed body’s protein synthesis needs are degraded
• Proteins in the body are broken down to supply amino acids for catabolism when carbohydrates are in short supply

Question 34

Describe the enzymatic hydrolysis of dietary proteins.

Answer 34

• Pepsin: proteins to peptides in stomach
• Trypsin/chymotrypsin: proteins & larger peptides to smaller peptide in small intestine
• Aminopeptidases/carboxypeptidases A and B: peptides to amino acids in small intestine

Question 35

What maintains a steady supply of amino acids?

Answer 35

Digestion of dietary proteins in the intestine and the degradation of proteins within cells

Question 36

What role does the stomach play in amino acid digestion?

Answer 36

Acidic environment and enzymes produce free amino acids and di/tri- peptides

Question 37

What role does the intestine play in amino acid digestion?

Answer 37

Membrane bound proteins (aminopeptidases) degrade protein down further

Question 38

What are cellular proteins targeted for destruction used to degrade?

Answer 38

• Misfolded proteins
• Foreign proteins
• Unwanted proteins